Final answer:
Increased oxygen demand in a normal heart is supplied by vasodilation of the coronary arteries, which allows more blood and oxygen to reach the heart muscle.
Step-by-step explanation:
Increased oxygen demand in a normal heart is supplied by vasodilation of the coronary arteries. The coronary arteries perform a critical function by supplying oxygen-rich blood to the heart muscle (myocardium). During periods of increased demand, such as during exercise or stress, these arteries can widen, or dilate, to allow more blood to flow to the heart muscle.
Vasodilation of coronary arteries increases the diameter of the blood vessels, which, in turn, increases blood flow and the supply of oxygen and nutrients to the heart muscle. Other options like vasoconstriction would reduce blood flow, while collateral circulation can provide an alternate route for blood flow if the main pathway is blocked. Atherosclerosis is a condition where arteries become narrowed and hardened due to plaque build-up, and it is not a mechanism that supplies oxygen but rather a pathological condition that impairs blood flow.